Water heaters come with a thermostat to adjust the temperature of water. When the set temperature is reached, the burner in gas powered water heater or the electric coil in electric water heater is turned off. When the temperature drops below the set temperature, the water heater is turned on again. This process repeats all the time. The user sets the temperature high enough to get hot water during periods of peak usage even on the coldest day of the year. This temperature is maintained during the day as well as night when there is not much need for hot water. People seldom change the setting of the thermostat. Hence the high temperature is maintained even during summer. This results in wastage of fuel. This also shortens the life of the water heater. There is a need for a programmable thermostat that can be programmed to heat water in the morning to the required high temperature, then turn down the thermostat during daytime when there is no one in the house to use hot water, turn it up again to a moderate temperature in the evening for dinner time usage and turn it down for the night. Since there are already millions of water heaters in use, the programmable thermostat should be easy to install on an existing water heater.
In U.S. Pat. No. 6,920,843, William Wilson uses a solenoid in the gas supply line to interrupt supply of gas. It has two drawbacks. The first is that the user will have to get the unit installed by a licensed plumber. The second drawback is that the manufacturer warranty may be voided since we are tampering with the original design of the product. So this is not a practical one. In U.S. Pat. Nos. 7,380,522 and 6,375,087, the system has to be built in by the manufacturer. It cannot be attached to the millions of water heaters already in use.